The research presents an assessment of the open spaces in Barcelona in the mid-19th century based on a detailed look at the map that the architect Miquel Garriga i Roca laid between 1856 and 1862. The cartography determined the size and measurements of the existing city at a time when the extension towards the contiguous agricultural plain was being prepared on the basis of the Eixample plan drawn up by Cerdà (1859). The main objective of this research is to evaluate the environmental quality of the city at that time and compare it with the conditions of the same urban fragment today, based on the analysis of (1) streets and pavements; (2) squares and new esplanades on the edge between the old town and the new modern city; (3) ventilation shafts, courtyards and gardens. The analysis carried out both graphically and quantitatively shows the different stages of habitability that the urban structure provided to the consolidated fabric. Although the object of research is seen in perspective, the value of this work lies in the fact that, on the one hand, it places morphological analysis as a central tool for interpreting the (historical) city; on the other hand, it attempts to relate the roots of hygienism, which has re-emerged in the discipline in the wake of the recent COVID, to the image of the urban form.